Response and Recovery of Turbulent Pipeflow Past Square Bar Roughness Elements

• Author / Creator

  Goswami, Shubham

• This dissertation looks at the response and recovery of turbulent pipeflow past square bar roughness elements with two heights at Reynolds numbers of 5000 and 156000. The response of turbulent pipeflow to multiple square bar roughness elements is also evaluated at the higher Reynolds number using different Reynolds-Average-Navier-Stokes (RANS) models. Two roughness heights are considered for this study based on their relative position inside the boundary layer: h/D = 0.05 and 0.1, where h is the bar height and D is the pipe diameter. A validation and verification analysis enabled creating a benchmark on the performance of different RANS-based turbulence models in simulating non-equilibrium wall bounded turbulent flows. Using k-epsilon RANS model, which performed the best in the benchmark performance study, the effects of multiple roughness elements are examined using two separation patterns: periodic and scattered. The flow response and recovery are evaluated based on the variations in the mean and turbulent fields. It is determined that the mechanism of recovery is prolonged in the pipeflow perturbed by smaller roughness element of height h/D = 0.05. Increasing the number of roughness elements further prolong the flow recovery until it becomes asymptotic with three periodically separated square bars. The separation pattern of roughness elements has a negligible effect on the overall turbulent pipeflow response and recovery at a high Reynolds number. This study is then extended to the examination of viscoelastic effects on the response and recovery of turbulent pipeflow past a single roughness element with two heights using the Finitely Extensible Non-linear Elastic-Peterlin (FENE-P) rheological model incorporated into Direct Numerical Simulations (DNS) at Reynolds number of 5000. These simulations revealed the importance of viscoelastic characteristics in significantly altering the overall flow response and recovery compared to Newtonian flow. The viscoelastic fluid properties correspond to a high polymer-additive concentration solution. For both bar heights examined here, the viscoelastic flow experiences significant reduction in the size of the recirculation region, which is also translated to a considerably faster recovery compared to the Newtonian flow. Moreover, the near-wall turbulence is reduced significantly due to the viscoelastic effects, which contributes to a lower wall friction, and thus, a lower drag.

• Subjects / Keywords

  • DNS
  • RANS
  • Computational Fluid Dynamics
  • pipeflow
  • Flow control

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-hgax-3316

• License

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